Binary and ternary metal-nonmetal compounds of various compositions are widely used as thin films for a variety of purposes. For example, binary and ternary metal-nonmetal compounds, including but not limited to Y2O3, ZrO2, YZO, HfO2, YHO, Al2O3, AlO2, ZnO, AZO, ITO, SiC, Si3N4, SixCyNz, SixOyNz, TiO2, CdS, ZnS, Zn2SnO4, SiO2, WO3, CeO3 and so on, have been deposited as thin film coatings or layers of multilayer film stacks serving to various purposes, such as transparent conductive oxide (TCO) electrodes, passivating films, back surface field layers, up- and down-converters, selective emitter masks, ion storage, solid electrolytes, moisture barriers, abrasion resistance layers, thermal barriers, impedance correction layers, surface modification and the like.
Many methods are known that provide for the deposition of these materials. Those methods can be divided into two categories: vacuum techniques such as PVD, CVD, ALD, MBE etc., and non-vacuum ones such as electroplating, CBD, screen printing, etc. The vacuum techniques have high capital expenses, cost of operation and cost of consumables. The non-vacuum techniques have high capital expense and waste treatment costs and are very limited in many ways.
The use of sol-gels provides an alternative to the foregoing. Sol-gel precursors have the unique ability to undergo polymerization to form ultrapure continuous films with exact stoichiometry and doping thereby providing means for microstructure and interface engineering. Currently sol-gels are used mainly for the small scale applications such as optical lenses or biomedical devices such as implants and vascular stents. Sol-gel precursor solutions are typically applied to the lens or biomedical device by dip, spin or spray coating. Roll coaters have not been used successfully in the deposition of large scale sol-gel based thin films because of the difficulties in forming and maintaining a dynamic wetting line using non-Newtonian fluids.
There are many roll coater designs know in the art. However, in large part, such designs do not enable the industrial deposition of many critical thin films using sol-gel precursors.
Accordingly, there is a need for systems and methods that can provide aforementioned binary, ternary and other compounds as a single layer or multilayer film stack member on large size flat substrates, both rigid and flexible without compromising the nanocomposite films' purity, stoichiometry, morphology and thickness uniformity.
There is an additional need to provide roll coaters that can efficiently use sol-gel precursors with minimal loss of material.
There is also a need for a means to provide preventative maintenance of roll coater components, such as applicator rolls used with sol-gel precursor solutions.